Fresh water dissolvable aluminum alloy

ABSTRACT

A dissolvable aluminum alloy can be used for components of a downhole tool in hydraulic fracturing operations with low salinity fluid at low temperatures, including fresh water. The dissolvable aluminum alloy can be dissolved completely and controlled at a dissolving rate compatible with hydraulic fracturing operations. The alloy comprises aluminum having grain boundaries, magnesium at 8.25-12% by weight, gallium at 2.5-4% by weight, and indium at 2-4% by weight. At least portions of magnesium, gallium, and indium are located in the grain boundaries. There are secondary phase particles, including Al—Mg Beta, Mg2Si, Mg and Al—Ga Gamma phases at the grain boundaries.

CROSS-REFERENCE TO RELATED APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

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BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a material composition in the oil and gas industry. More particularly, the present invention relates to dissolvable metal alloys to form components of downhole tools. Even more particularly, the present invention relates to a fresh water dissolvable aluminum alloy for components in hydraulic fracturing operations.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

Downhole tools are commonly used in oil and gas production. A borehole is drilled through a ground formation, and downhole tools, such as plugs and sleeves are positioned along and within the borehole. The plugs close and open portions of the borehole so that a zone of ground formation can be isolated. A sleeve opens and closes to make the fluid connection between the borehole and the ground formation. The downhole tools work to isolate and connect the zone for various operations to prepare and produce the hydrocarbons from the ground formation. When the operations are complete in the zone, components of the downhole tool or even the entire downhole tool may require removal. For example, a dissolvable frac ball set in a plug to trigger a seal may be removed by injecting a solvent targeted to the dissolvable frac ball so that the seal is removed. Alternatively, the entire plug may be removed.

Dissolvable alloys were developed for the manufacture of downhole tool components in the oil and gas industry. There are mainly two types of dissolvable alloys: magnesium and aluminum based alloys. The fresh aluminum alloys are chemically active in atmosphere. A dense and full oxidation layer is formed on the aluminum alloy, when exposed to the atmosphere. The oxidation layer prevents further reaction with oxidation beneath the surface with the oxidation layer. Therefore, these fresh aluminum alloys are not able to be used as dissolvable metal alloys for downhole tool components due to the limited dissolvability. The special elements, such as Sn, Ga and In are added to the aluminum alloy. These low-melting point elements are able to break the oxidation layer, so that the oxidation will proceed until the alloy is dissolved.

Generally being dissolvable is not automatically useful for components of downhole tools. Oil and gas production can span a wide range of conditions with vastly different temperatures, pressures, and fluid environments. The disclosure of dissolvable metal alloys, and particularly, dissolvable aluminum alloys are known in the prior art intended for a variety of conditions. U.S. Pat. No. 9,757,796 issued on 12 Sep. 2017 to Sherman et al and U.S. Pat. No. 8,211,248, issued on 3 Jul. 2012 to Marya both disclose dissolvable aluminum alloys.

In some hydraulic fracturing processes, the use of lake water or ground water as fracturing fluid requires components of downhole tools to be compatible with fresh water or water with low salinity and low temperatures. The dissolvable metal alloys for components in high salinity fluids or in high temperature environments are not compatible with hydraulic fracturing with ground water. Specific dissolvability for certain conditions is not disclosed by general dissolvability. Different factors can control whether the alloy dissolved, including environmental conditions and material composition.

It is an object of the present invention to provide a dissolvable aluminum alloy.

It is another object of the present invention to provide a dissolvable aluminum alloy for components of a downhole tool.

It is another object of the present invention to provide a dissolvable aluminum alloy compatible for fresh water or at least low salinity fluid.

It is still another object of the present invention to provide a dissolvable aluminum alloy compatible for fresh water or at least low salinity fluid at low temperatures.

These and other objectives and advantages of the present invention will become apparent from a reading of the attached specification.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include a dissolvable alloy for components of a downhole tool. The alloy comprises aluminum having grain boundaries, magnesium at 8.25-12% by weight, gallium at 2.5-4% by weight, and indium at 2-4% by weight. At least portions of magnesium, gallium, and tin are located in the grain boundaries so as to be dissolvable at low salinity and low temperatures, including fresh water. There are secondary phase particles comprised of 10 Mol. % of Al—Mg Beta, 2.3 Mol. % Mg2Si, 0.85 Mol. % Mg and 0.2 Mol. % Al—Ga Gamma phases. A dissolvable aluminum alloy is not inherently dissolvable at low salinity and low temperature, and the dissolving rate can be controlled so as to be compatible with hydraulic fracturing operations.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph illustration of phase simulation results by CALPHAD modeling software.

FIG. 2 is an X-Ray Diffraction Phase Identification of the dissolvable aluminum alloy of the present invention.

FIG. 3 are scanning electron microscope views of the Al matrix and the secondary phases along the grain boundaries of the Al matrix of the dissolvable aluminum alloy of the present invention.

FIG. 4 are photos (a), (b), and (c) of a dissolvable aluminum alloy of the present invention, and a graph illustration (d) of the dissolution rates being dissolved in 1 wt. % KCI at 60° C., 3 wt. % KCI at 50° C., deionized water at 50° C., and at 1 wt. % KCI at 93° C.

FIG. 5 is a graph illustration of tensile tests of the dissolvable aluminum alloy of the present invention after different post processes: AR—as received, AG—aged at 180° C.; HIP450-hot isostatically pressed at 450° C.; and HIP510-hot isostatically pressed at 510° C.

FIG. 6 is a graph illustration of a compression test of the dissolvable aluminum alloy of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-6 show the dissolvable aluminum alloy of the present invention in the conditions for hydraulic fracturing operations in low salinity fluid at low temperatures, including fresh water. There is a critical limitation to dissolvability. Aluminum alloys are already chemically active in atmosphere, and the chemical activity is so fast that the oxidation layer forms to prevent dissolution. A passivation layer forms in the prior art conventional aluminum alloy, and dissolution stops. The present invention addresses the need to pass the critical limitation.

Embodiments of the dissolvable aluminum alloy in FIGS. 1-3, show a dissolvable alloy for components of a downhole tool of the present invention. The dissolvable alloy comprises aluminum having grain boundaries, magnesium at 8.25-12% by weight, gallium at 2.5-4% by weight, and indium at 2-4% by weight. The Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS) mapping of FIG. 3 show at least portions of magnesium, gallium, and tin located in the grain boundaries. The mapping shows that these additives to the aluminum are mainly sited on the grain boundaries, as shown in FIG. 3. These additives create the micro-scale galvanic corrosion with the Al matrix. Especially, the Mg-rich, Sn-rich, In-rich and Ga-rich phases are found in these locations. Among these elements, the low melting point Sn, In and Ga elements are the main contributors to attack the oxidized surfaces of aluminum, especially from the grain boundaries as shown.

FIG. 1 uses CALPHAD phase simulation modeling software to identify Al—Mg Beta, Mg2Si, Mg and Al—Ga Gamma phases as secondary phases in the dissolvable aluminum alloy of the present invention. FIG. 2 confirms the top three main phases of Al matrix, Al—Mg Beta and Mg2Si by X-Ray Diffraction phase identification. FIG. 1 further specifies 10 Mol. % of Al—Mg Beta, 2.3 Mol. % Mg2Si, 0.85 Mol. % Mg and 0.2 Mol. % Al—Ga Gamma phases.

FIG. 4 confirms that the dissolvable aluminum alloy of the present invention in FIGS. 1-3 passes the critical limitation so that full dissolution can be achieved. The entire component of the downhole tool must be dissolved. Remnants and partial components would disrupt operations. The dissolvable aluminum alloy of the present invention is dissolvable in 1 wt. % KCI at 60° C. with a dissolving rate less than 100 mg/cm2/hr (specifically, about 75 mg/cm2/hr) for more than seven hours. The dissolvable aluminum alloy of the present invention is dissolvable in 3% KCI at 50° C. with a dissolving rate of about 45 mg/cm2/hr. The dissolvable aluminum alloy of the present invention is dissolvable in deionized water at 50° C. with a dissolving rate less than 50 mg/cm2/hr (specifically, about 30 mg/cm2/hr). This level of performance by the composition of the present invention is not disclosed by the prior art.

It is acknowledged that the prior art, specifically, U.S. Pat. No. 8,211,248, discloses some ranges of common components, such as magnesium at 0.5-8.0% by weight and gallium at 0.5-8.0% by weight, as well as indium at 0.1-2.1% by weight. Specific examples in the prior art show magnesium at 3.5% by weight, gallium at 1.6% by weight, and tin at 0.15% by weight, as well as indium at 0.3% by weight and copper at 1.45% by weight, silicon at 0.15% by weight and others at 0.3% by weight. Magnesium, gallium, and tin as additives are known for dissolvable aluminum alloy, although there is no overlap of the claimed ranges.

Even with known additives, the present invention passes the critical limitation in order to complete dissolution and achieves that unexpected result with common components as magnesium, gallium and tin as additives to the dissolvable aluminum alloy of the present invention. FIG. 4 shows the unexpected result of adding higher amounts of low melt additives (Mg, Ga, Sn) to suitable dissolution rates to avoid the passivation layer problem at lower temperature or lower salinity or both, including fresh water. The present invention also shows the dissolution rate of about 250 mg/cm2/hr in 1 wt. % KCI at 93° C., indicating suitability for components requiring higher dissolution rates than others in the same conditions without the passivation layer problem. The present invention adds more magnesium together with more gallium to increase dissolution rates. The low temperature was not the only factor to slow dissolution rates, as shown by FIG. 4. The salinity at very low level can hamper the dissolvability of prior art dissolvable materials, including magnesium and aluminum dissolvable alloys. The aluminum alloys of the present invention, on the other hand, can achieve the suitable dissolvability in de-ionized water at 50° C. When comparing the dissolvability in the condition of 3% KCI at 50° C., the dissolvability of the present invention is minimally affected by the salinity up to 3% KCI. The insensitivity of dissolvability to the salinity is of significance to simplify the hydraulic fracturing tools and process, as the salinity of fracturing fluid varies significantly from one well to another, even in the same well pad. The present invention demonstrates the dissolvable aluminum alloys can have suitable dissolving rates, avoiding the critical slowness of dissolving rates and quickness that lead to passivation layers. The present invention achieves a dissolving rate suitable for the applications at low temperature and low salinity, even in fresh water.

The sample of dissolvable aluminum alloy of the present invention in FIG. 4 is comprised of aluminum, magnesium is 8.5% by weight, gallium is 5.0% by weight, and indium is 3.0% by weight. The sample is further comprised of 2.0% by weight tin, 0.3% silicon and 0.2 manganese as other additives. FIG. 4 supports the unexpected result of dissolution at the suitable dissolution rate in low salinity and low temperature conditions, such as fresh water.

FIGS. 5 and 6 show the dissolvable aluminum alloy of the present invention as suitable for components of downhole tools. The strength of dissolvable metal alloy was not sacrificed in order to be dissolvable in fresh water. Post-processing treatment of the dissolvable aluminum alloy of the present invention increases strength and elongation for use in components of downhole tools. An aging heat treatment applied in FIG. 5. The tensile test of a sample as received (AR) and aged (Ag) conditions are shown in FIG. 5. The tensile test of as-received AG shows 200 MPa ultimate tensile strength and 1.5% elongation. The aging heat treatment does not improve the strength or elongation. On the other hand, a hot isostatic process (HIP) at 450° C. and 510° C. was also applied to the dissolvable aluminum alloy of the present invention. The HIP at 450° C. shows the improvement on the strength to 240 MPa and elongation to 2.6%.

FIG. 6 shows the compression test of the dissolvable aluminum alloy of the present invention. The sample was buckled at 0.15%. Therefore, the compression strength is determined to be about 420 MPa before the corresponding buckling. Thus, the dissolvable aluminum alloy of the present invention is sufficiently high for some downhole tool components under compression state.

The present invention provides a dissolvable aluminum alloy for components of a downhole tool. The alloy remains sufficiently strong so as to be formed into a component and functional as a downhole tool. The dissolvability is controlled for low salinity at low temperatures, which correspond to fresh water. The dissolvability in these environmental conditions allow for use in hydraulic fracturing operations with ground water or other sources, such as lake water. Effective dissolvability in fresh water or at least low salinity fluid at low temperatures allows for use of the present invention in many wells, in which the slow dissolvability is a consideration with low salinity fracturing fluid. The present invention achieves a critical dissolving rate needed in hydraulic fracturing operations with fresh water. Prior art compositions may be adjusted for any dissolving rate; however, the present invention finds the unexpected result of adding more low melt elements as additives to achieve the desired faster dissolution rate within the critical range for fresh water.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated structures, construction and method can be made without departing from the true spirit of the invention. 

We claim:
 1. A dissolvable alloy for components of a downhole tool, comprising: aluminum having grain boundaries; magnesium at 8.25-12% by weight; gallium at 2.5-4% by weight; and indium at 2-4% by weight, wherein at least portions of magnesium, gallium, and indium are located in said grain boundaries so as to be dissolvable a salinity between 0-3% by weight at temperatures between 50-60° C. with a dissolving rate less than 100 mg/cm2/hr.
 2. The dissolvable alloy of claim 1, wherein said aluminum, said magnesium, and said gallium are comprised of secondary phases, said secondary phases being Al—Mg Beta phases, Mg phases, and Al—Ga Gamma phases.
 3. The dissolvable alloy of claim 2, wherein at least portions of said secondary phases are located in said grain boundaries.
 4. The dissolvable alloy of claim 2, wherein said secondary phases are comprised of 10 Mo. % Al—Mg Beta phases, 0.85 Mol. % Mg phases, and 0.2 Mol. % Al—Ga Gamma phases.
 5. The dissolvable alloy of claim 1, further comprising: silicon at 0.2-0.4% by weight.
 6. The dissolvable alloy of claim 5, wherein said aluminum, said magnesium, said gallium, and said silicon are comprised of secondary phases, said secondary phases being Al—Mg Beta phases, Mg2Si phases, Mg phases, and Al—Ga Gamma phases.
 7. The dissolvable alloy of claim 5, wherein said secondary phases are comprised of 10 Mo. % Al—Mg Beta phases, 2.3 Mol. % Mg2Si, 0.85 Mol. % Mg phases, and 0.2 Mol. % Al—Ga Gamma phases.
 8. The dissolvable alloy of claim 1, further comprising: tin at 1.0-3.0% by weight.
 9. The dissolvable alloy of claim 1, further comprising: manganese at less than 0.2% by weight.
 10. The dissolvable alloy of claim 1, wherein magnesium is 8.5% by weight, wherein gallium is 5.0% by weight, and wherein indium is 3.0% by weight.
 11. The dissolvable alloy of claim 1, wherein the dissolving rate is 20-40 mg/cm2/hr in deionized water at 50° C.
 12. The dissolvable alloy of claim 1, wherein the dissolving rate is 35-55 mg/cm2/hr in 3% KCI at 50° C.
 13. The dissolvable alloy of claim 1, wherein the dissolving rate is 60-90 mg/cm2/hr in 1% KCI at 60° C.
 14. The dissolvable alloy of claim 1, wherein the dissolving rate is 240-400 mg/cm2/hr in 1% KCI at 93° C. 